The problem of corrosion of non-metallic inorganic items, such as glassware, ceramic and enamel materials, when subjected to automatic dishwashing processes is well recognised in the art. For example, it has been proposed that the problem of glassware corrosion is the result of two separate phenomena. Firstly, it has been suggested that the corrosion is due to leakage of minerals from the glass network, accompanied by hydrolysis of the silicate network. Secondly, it is proposed that the silicate material is then released from the glass.
These phenomena can cause damage to glassware after a number of separate wash cycles. The damage may include cloudiness, scratches, streaks and other discoloration/detrimental effects.
Silicate materials have been proposed as agents that are effective in preventing materials from being released by the glass composition. However, the use of silicate compounds can have detrimental side effects, such as the tendency to increase separation of silicate material at the glass surface.
A further solution has been to use metals such as zinc, either in metallic form (such as described in U.S. Pat. No. 3,677,820) or in the form of compounds. The use of soluble zinc compounds in the prevention of glassware corrosion in a dishwasher is described in, for example, U.S. Pat. No. 3,255,117.
European Patents; EP-A-0 383 480, EP-A-0 383 482 and EP-A-0 387 997) describe the use of water insoluble compounds including zinc silicate, zinc carbonate, basic zinc carbonate (Zn2(OH)2CO3), zinc hydroxide, zinc oxalate, zinc monophosphate (Zn3(PO4)2) and zinc pyrophosphate (Zn2P2O7) for this purpose.
Bismuth has been used as an additive to aid the prevention of corrosion of glazed glassware corrosion. For example, BE 860180 describes the use of bismuth to avoid damage of decorated, glazed articles.
The value of bismuth in this purpose has been diminished by the detrimental effects that the use of bismuth compound has on other components of the washing process or detergent composition. In soluble bismuth compounds can cause the formation of stains on kitchenware items e.g. glassware and cutlery which come into contact with these compounds. For these reasons the use of bismuth alone as a glaze protector has been avoided, although a combination of zinc and bismuth has been found to address this issue (see WO-A-04/106476).
However, it has been found that the use of heavy metal compounds in some circumstances reduce the bleaching performance of a dishwashing composition on bleachable stains such as tea stains. Furthermore, for environmental reasons, it is becoming increasingly desirable to limit (and especially to avoid) the use of heavy metals in detergent formulations.
WO2010/020765 proposed a solution to this problem of glass and tableware erosion that did not require the use of heavy metals. This document, which is hereby incorporated by reference, disclosed that polyalkyleneimines were highly effective additives for the prevention of corrosion of non-metallic inorganic items in automatic washing machines.
However, further to this, it has since been found that while the polyalkyleneimines do improve the corrosion protection their use has unexpectedly been found to cause poor rinse performance. This leads to unattractive spotting on glassware.
It is the object of the present invention to overcome the poor rinse performance that accompanies the use of polyalkyleneimine formulations.